(prometheus) add explanation about incompatibility of metric find query

docs/sources/datasources/prometheus.md

@@ -51,6 +51,8 @@ Name | Description
 
 
 For details of `metric names` & `label names`, and `label values`, please refer to the [Prometheus documentation](http://prometheus.io/docs/concepts/data_model/#metric-names-and-labels).
 For details of `metric names` & `label names`, and `label values`, please refer to the [Prometheus documentation](http://prometheus.io/docs/concepts/data_model/#metric-names-and-labels).
 
 
+> Note: The part of queries is incompatible with the version before 2.6, if you specify like `foo.*`, please change like `metrics(foo.*)`.
+
 You can create a template variable in Grafana and have that variable filled with values from any Prometheus metric exploration query.
 You can create a template variable in Grafana and have that variable filled with values from any Prometheus metric exploration query.
 You can then use this variable in your Prometheus metric queries.
 You can then use this variable in your Prometheus metric queries.